Photoionisation of multiply-charged ions in the VUV and X-ray energy ranges

Since experimental results other than energy levels are still scarce for multiply charged ions, this paper will be essentially devoted to a review of theoretical results relative to photoinisation cross sections for ions and to a discussion of their reliability in terms of the main physical approximations introduced in the atomic models. Photoionisation of both inner and outer shells of ions are considered here (from a few eV. up to 20 or 50 keV according to the atomic number). Within this framework, several important points will be emphasized: a) the general trends displayed by the variation of the various cross sections within isoelectronic and isonuclear sequences, b) the various theoretical models currently used and their limitations, c) some crucial problems and unresolved difficulties will be pointed out, especially for ionic configurations involving open subshells (2p,3d,4d)